已知(x+y)的平方=4(x-y)的平方=10求x的平方加y的平方和xy的值

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不知你的题意?
若：
(x+y)²=4
(x-y)²=10
∴x²+y²
=[(x+y)²+(x-y)²]÷2
=(4+10)÷2
=14÷2
=7
xy
=[(x+y)²-(x-y)²]÷4
=(4-10)÷4
=(-6)÷4
=-1.5
若题目是：(x+y)²=4(x-y)²=10
则：(x-y)²=10/4=2.5
∴x²+y²
=[(x+y)²+(x-y)²]÷2
=(10+2.5)÷2
=12.5÷2
=6.25
xy
=[(x+y)²-(x-y)²]÷4
=(10-2.5)÷4
=7.5÷4
=1.875